A cost flow model, such as an Activity-Based Costing (ABC or ABM) model, is a multi-dimensional directed graph. It depicts how money flows in an enterprise. The nodes in the graph represent the resource, activity, or cost object accounts. The edges in the graph have a percentage on them, which defines how much money flows from a source account to a destination account. This graph can easily have hundreds of thousands of accounts and millions of edges.
People want to know, not just how much money flowed to an account, but how much money account A contributed to account B. If there are 100 accounts of type A and 100 accounts of type B, there are 10,000 possibilities of contribution from accounts of type A to accounts of type B. Situations could even include over a quadrillion (1×1015) possibilities. It is impossible or impractical to write out all the values. A further restriction might arise in some situations that the reporting tools available are based on table structures that require the graph to be forced into a regular structure so that it can be used by existing reporting and database tools, such as relational database management systems (RDBMS), multi-dimensional database systems (MDDB) (e.g., Online Analytical Processing (OLAP) tools), etc.